Receiving system for modulated waves



2 Sheets-Shet 1 INVENTOR {r k i A O Nw' I I I I I III- I'll!llllllllllll;

F. K. VREELAND Filed Aug. "17, 1928 A AAAAAAA AAAAAAA Feb. 3, 1942.

RECEIVING SYSTEM FOR MQDULATED WAVES mix FE m 6 RV Feb. 3, 1942. F. K.VREELAND 2,272,075

RECEIVING SYSTEM F03 MODULATED WAVES Filed Aug. 17, 1928 2 Sheets-Sheet2 Patented Feb. 3, 1942 Frederick K.Vreelan'd, Montclair, N. J.Application August 17, 1928. Serial No. 300,172

The inventionherein described relates to' receiving systems for radiantenergy.

The particular object of the invention is to secure distcrtionlessreception and amplification of the band of transmitted frequenciesincluded in a modulated signal wave and to'permit ready adjustment ofthe position of the band of reception in the frequency scale to includethe band of transmission frequencies of a desired signal and to excludeundesired frequencies.

One means. of accomplishing this is disclosed in my U. S. Patent No.1,666,518 which includes a band receiving system comprising an amplifierwhose gain is substantially. uniform over a band of frequencies togetherwithmeans for shiftin of the band of effective amplification inthefrequency scale. In my Patent No. 1,682,8'741 have When the positionof the band of selected frequenciesis shifted in the frequency scale itis important that the'band of amplification shall be uniform also ineach position of the banddescribed an improved band amplifier includingmeans for continuously varyingv the position of quencies.

of response of the selector. One means of accomplishing thiswas setforth in my application last-named and included the use of. a radiofrequency amplifier having also a uniform band "characteristic, andshifting the'positions of the bands of reception of the band selectorand the band amplifier simultaneously in the frequency scale. Thisrequires ,co-ordination of adjust ment between the band selector and theband amplifier. Such co-ordination is avoided in another arrangementshown in the same application in which the band selector is combinedwith an aperiodic amplifying and detecting system.

- Such a system meets the requirements above ex Anothertype of bandreceiving system is described in my Patent No. 1,725,433 including aband selector which receives with substantial uniformity a band offrequenciesand excludes undesired frequencies and in an embodiment ofthat invention shown the frequency selection of the band selectoroperates independently of the amplifier. Specifically I have shown andclaimed in that patent the use of such a band selector in cooperationwith an aperiodic amplifying and de-' quency amplifier which issubstantially aperiodic and has a response curve which is substantiallyfiat or uniform over any band of frequencies included'in any modulatedsignal wave within the range of adjustment of the band selector andwhose response curve is preferably substantially uniform over the entirerange of frequencies to be received.

The present invention'has important advan tages; In the first place, inorder to take full advantage of the property of the band selector ofreceiving with substantial uniformity all' of the frequencies includedin the band of the modulated signal wave, it is necessary that theamplification of such frequencies shall be uniform.

It contemplates lector units. invention the plurality of band selectorunits plained of amplifying without distortion any band of selectedfrequencies and permitting the adjustment of this band in thefrequencyscale, without requiring adjustment of the amplifying and detectingsystem.

The specific improvement of the present invention resides in theinclusion in an aperiodic amplifying and detecting system of anaperiodic radio frequency amplifier and also in the use of otherfeatures that increase the effectiveness of this combination-as willappear hereinafter.

I have found that it is feasible to construct an amplifier of this typewhich is highly eificient and whose response curve is substantiallyuniform over the full range of adjustment of the band selector.

The use of such an amplifier makes possible a high sensitivity in thereceiving system, particularly when a large number of stages areemployed with a relatively small gain per stage. In fact a sensitivityhas been obtained fully equal to that accomplished by tuned radiofrequency amplifiers.

In order to take advantage of the highest sensitivity of the aperiodicamplifier it is usually desirable to increase the selectivity of theband selector by employing a plurality of band se- In one embodiment ofthe present are coupled in cascade in advance of the aperiodic radiofrequency amplifier. other arrangement one or more of the units placedin advance of the aperiodic amplifier and another one or more unitsinserted behind the amplifier or a part thereof. Other possiblemodifications will be readilyunderstocd.

In an- 1 In the drawings Figure 1 represents a simple embodiment of theinvention.

Figure 2 represents another embodiment including a second band selectorfollowing the aperiodic amplifier.

In Figure 1 S182 represent two band selector units. These units as shownare of the type set forth in my Patent No. 1,725,433 which includes tworeactive couples X1Xz combined with a band forming reactance X: commonto both couples, whereby the system is made responsive with substantialuniformity over a definite and limited band of frequencies. These twoband selector units are coupled by a coupling means which issufficiently loose not to impair their band selective quality. In thearrangement shown the coupling means comprises a loop circuit includingcoils MN coupled to both band selectors. This arrangement is desirablesince it permits individual shielding of the two selector units asindicated by the broken lines, and also reduces the transmission ofshock' pulses producing ground noise, but any suitable form of couplingmay be substituted. The value of the coupling reactances is so relatedto the reactances of the The first band selector, which is doubletuned,-

is employed as a pre-selector in advance of the first amplifier tube andis operatively associated with a suitable signal collecting means whichis here shown as an antenna A coupled with the band selector in themanner explained in my co-pending application last referred to. The

second band'selector is operatively associated with an aperiodic radiofrequency. amplifier. In the arrangement shown the selector is coupledto the amplifier by an aperiodic coupling coil H, as fully explained inmy said'co-pending application.

The aperiodic amplifier shown comprises amplifier tubes RF-l, RF2 and adetector tube D. The mode of coupling of the tubes here shown is thatemploying impedances 21, 22, located respectively in the output circuitof one tube and the input circuit of the next tube, with a bridgingcapacity C which passes the radio frequency impulses from one'tube tothe next. Bypass condenser C1 and choke coils L1 are desirable toprevent interaction between the stages.

If the impedances 2122 are large, as they are preferably, or if theyhave lar e resistance, the amplifier is substantially aperiodic.

system is then responsive to another band of frequencies. Because of theaperiodic character of the radio frequency amplifier any band offrequencies so selected is amplified with substantial uniformity, sothat the selected signal is received without distortion.

The variable elements of the band selector units, here shown ascondensers, are mechanically coupled so that they may be adjustedsimultaneously and similarly by a single move-' tion bands. The onlyeifect of this will be to narrow slightlythe overall band of reception.It causes no loss of signal strength, as occurs with tuned resonantcircuits. This is an important practical feature of the presentinvention.

In order to utilize the particular features of this invention that givedistortionless selection and amplification of a modulated wave, andstill permit the reception of signal waves ranging from feeble distantsignals to the most powerful ones, it is important to have meansfor-controlling the responsiveness of the system without impairing theuniformity of its response. The preferred mode of accomplishing this isto regulate the gain of the radio frequency amplifier by controlling thespace current in the tubes. This arrangement takes full advantage of theunusual capabilities of this invention of securing high selectivity fora band of frequencies together with extreme sensitivity in theamplifier. The specific arrangement shown includes a variable impedanceinserted in series with the anode supply whereby the current or voltageor both supplied to the tubes is controlled. The preferred form ofvariable impedance is a ballast tube shown at B in the drawings,preferably of the thermionic type having an anode a, cathode is, and acontrol electrode 9. The effective impedance of the ballast tube iscontrolled by impressing an adjustable electromotive force on thecontrol electrode 9 of the tube, as for example by means of the batteryand potentiometer Er The operation of the apparatus is as follows:

Signal impulses whose frequencies lie within a definite band offrequencies are passed with substantial uniformity by the first bandselector S1, and frequencies outside the band are to a large extentexcluded. The same band of frequencies is received and passed withsubstantial uniformity by the second band selector S2, and any remnantof interfering frequencies outside the band is still further reduced bythe selective action of the selector. The band of frequencies thusselected is applied to the radio frequency amplifier, which amplifiesthem without distortion.

When it is desired to select a different band of transmittedfrequencies, the band of response of the selector or selectors S1 and S2is shifted in the frequency scale by simultaneous and similar adjustmentof their reactances, and the battery and potentiometer shown.

shown. This mode-of controlling the output of the system enables thegain of the amplifier to be varied over very wide limits from thehighest amplification obtainable to a point where the signals are notamplified but are in fact reduced in strength, and this wide variationof gain is accomplished without sensible distortion of the signals, thatis, without material variation in the uniformity of amplification of allfrequencies included in the modulation band. When a considerable numberof stages are so controlled the range of sensitivity that may beobtained without distortion is enormous.

This means of controlling the gain of the amplifier is set forth atlength in my Patent No. 1,926,129, issued September 12, 1933, whichshows in addition automatic governing means whereby the amplifier iscontrolled automatically through the agency of the regulating tube B. Itwill be understood that the automatic features of the last namedapplication may be employed to supply the electromotive force Er, inplace of the In the arrangement shown in Figure 2 the iperiodic radiofrequency amplifier, including the itages RFI, RF-2, BI -3, is insertedbetween be two band selector units $182 as shown. In ;his arrangementthe first band selector is shown associated with the collector by acoupling tube ['1. Since this coupling tube prevents the introiuction ofan indeterminate reactance by the. :ollector' into the band selectorsystem, means for compensating the antenna reactance are not requiredand hence are omitted.

The arrangements shown in the drawings are chosen for illustration astypical embodiments of the invention but it will be understood that theinvention is not limited to thesespecific arrangements but issusceptible of a variety of applications.

I claim as my invention:

I In a receiving system for modulated signal waves, an amplifiercomprising a plurality of amplifier tubes arranged in cascade relation,a pre-selector with collecting means in operative relation therewith inadvance of the first; tube with respect to received waves and comprisingtwo,- reactive couples each having variable reactancescoupling meansbetween two: of. said amplifier tubes comprising two reactive:- coupleseach having variable reactances, and substantially aperiodic couplingmeans between. others of said amplifier tubes.

2.. In a receiving system for modulated radio frequency energy thecombination of two reactive. couples tuned; toa frequency of saidenergy, means for impressing said energy on one of said; couples, acoupling reactance; common to, both couples whose: value is so; relatedto the reactances of the. couples as to effect. highly uniform andselective transfer of the: modulated en'- ergy through a frequency rangecorresponding substantially to the range of audio frequencies, means forshifting the position of the frequency range of the. energy transferinthe frequency scale, and an amplifier aperiodically coupled with theother of said reactive couples and adapted ances wherebythe position ofthe band of response is shifted in the frequency scale, and an amplifieraperiodically coupled in cascade with one of said=selector unitsandiadapted toiamplify with substantial uniformity,- all frequenciesin-- cludediimany band passed by the band selectors.

4. In a receiving system; for; modulated? radiofrequency energy thecombination of a collector, a preselector' comprising two reactivecouples. tuned tea frequency of said ener y, means for impressing; theenergy received 'by the; collector on one. of. said couples, a couplingreactance common to both couples whosez value is sorelated tothereactancesof the couples as to effect, highly uniform andselectivetransfier of the modulated. energy" through a frequency rangecorresponding substantially to the range: of audio frequencies, means:for adjusting the neactances of the, two couples simultaneously andsimilarly thus: shifting the: range of the selectively transferred,energy in the frequency scale,jand an amplifier including a plurality ofamplifier tubes aperiodically coupled to the other of said reactivecouples for receiving signal impulses from the preselector andresponsive with substantial uniformity to all frequencies in anyfrequency range selected by the preselector.

FREDERICK K. VREELAND.

